<template>
<div class="scroll-container" ref="scrollContainer" @wheel.prevent="handleScroll" >
  <div class="scroll-wrapper" ref="scrollWrapper" :style="{top: top + 'px'}">
    <slot></slot>
  </div>
</div>
</template>

<script>
const delta = 15

export default {
  name: 'scrollBar',
  data () {
    return {
      top: 0
    }
  },
  methods: {
    handleScroll (e) {
      const eventDelta = e.wheelDelta || -e.deltaY * 3
      const $container = this.$refs.scrollContainer
      const $containerHeight = $container.offsetHeight
      const $wrapper = this.$refs.scrollWrapper
      const $wrapperHeight = $wrapper.offsetHeight
      if (eventDelta > 0) {
        this.top = Math.min(0, this.top + eventDelta)
      } else {
        if ($containerHeight - delta < $wrapperHeight) {
          if (this.top < -($wrapperHeight - $containerHeight + delta)) {
            this.top = this.top
          } else {
            this.top = Math.max(this.top + eventDelta, $containerHeight - $wrapperHeight - delta)
          }
        } else {
          this.top = 0
        }
      }
    }
  }
}
</script>

<style lang="less" scoped>
@import '../../styles/variables.less';

.scroll-container {
  position: relative;
  width: 100%;
  height: 100%;
  background: linear-gradient(to bottom, @bgColor, @bgColor + 5%);
  border-right: 1px solid #eaeaea;
  .scroll-wrapper {
    position: absolute;
     width: 100%!important;
  }
}
</style>
